EOVIST® is a paramagnetic contrast agent for magnetic resonance imaging (MRI), and is used for MRI of blood vessels, tissues, and other non-bony tissues, and particularly usefully, for diagnosis of an abnormality in the liver tissue. EOVIST® includes gadoxetate disodium as an active pharmaceutical ingredient, having a molecular weight of 725.72, an empirical formula of GdC23H28N3O11Na2, and a structural formula of gadolinium (4S)-4-(4-ethoxybenzyl)-3,6,9-tris(carboxylatomethyl)-3,6,9-triazaundecanoic acid disodium salt. Gadoxetate disodium has a structure of Formula (a) below in an aqueous solution.

In order to synthesize the compound of Formula (a), a method for synthesizing (S)-2,2′-(2-((2-(bis(carboxymethyl)amino)-3-(4-ethoxyphenyl)propyl)(carboxymethyl)amino)ethylazanediyl)diacetic acid, which is an intermediate from (S)—N1-(2-aminoethyl)-3-(4-ethoxyphenyl)propane-1,2-diamine, is disclosed in Chinese patent application publication No. CN104761461. However, there is no reference disclosing a method for preparing (S)—N1-(2-aminoethyl)-3-(4-ethoxyphenyl)propane-1,2-diamine trihydrochloride, which is used as a reactant, from 4-bromophenetole, which is a commercially available compound.